View Full Version : zenith 12a12c52 chassis television


damien191
03-06-2017, 11:38 PM
this came in for recycling a few weeks back where i work and i couldn't stand to see it dismantled - sortof works after replacing a belfuse there's a thin horizontal line - about two inches across the screen but that's about it for the vertical and i'm really not sure about how to go about fixing it, i sort of need somebody to hold my hand

aside from a soldering iron and a multi meter i have no tools and i'm better at black and white TV's and tube radios than color - that's why my roundie is still here not working either

anyone close to Evansville Indiana that wants to take a look?

damien191
03-06-2017, 11:46 PM
this is my first post here so sorry if i did anything wrong

also thought i would introduce the rest while i'm here

TUD1
03-07-2017, 12:29 AM
Welcome to the Forum! You did very well saving that Zenith from being murdered. If you're going to get into color TV, I highly recommend getting a good CRT tester, I use a Sencore CR70, and I love it. A receiving tube tester is also invaluable. I use a B&K 667, and it does the job well. I've solved many a problem in my tube sets, just by tracking down faulty tubes. A color NTSC generator is also a must. Near impossible to do good dynamic convergence without it. I use a Sencore VG91, and I love it also. Hope you get the Zenith running! Lot's of good assistance here. Be careful! They multiply!

damien191
03-07-2017, 12:39 AM
Welcome to the Forum! You did very well saving that Zenith from being murdered. If you're going to get into color TV, I highly recommend getting a good CRT tester, I use a Sencore CR70, and I love it. A receiving tube tester is also invaluable. I use a B&K 667, and it does the job well. I've solved many a problem in my tube sets, just by tracking down faulty tubes. A color NTSC generator is also a must. Near impossible to do good dynamic convergence without it. I use a Sencore VG91, and I love it also. Hope you get the Zenith running! Lot's of good assistance here. Be careful! They multiply!

since I've moved to a house with more space they seem to be finding me - it's honestly a money issue, i do what i can with what i have but i cant afford a bunch of the specific equipment i need

and like i said - i need someone to hold my hand on color sets, especially lacking a schematic or 90% of the knowledge many here have - someone had to tell me i could replace the belfuse with a pigtail - now how do i fix the vertical lol

TUD1
03-07-2017, 01:04 AM
I know how frustrating it is to be broke all the time, believe me. If it weren't for my two close TV friends, my collection would be virtually non existent. The sets are just getting super hard to find. I acquired most of my test equipment from my local radio club. I had to pay $100 for my CR70 though, and I don't regret it. It has totally replaced my B&K 470 as my main tester/rejuvenator.

Electronic M
03-07-2017, 08:04 AM
Welcome to VK!

I have almost that EXACT Zenith and an identical Silvertone roundy (plus a second similar earlier Silvertone roundy). My Zenith is a 12B13C52 chassis (may be covered in the same sam's) in the same cabinet (which was called the Boyden BTW). That Zenith can be a real work horse...Mine has been my main TV for 8 years (of heavy service), and aside from small occasional maintenance (focus divider, tubes, a couple of vert stage caps, the H out tube socket) it took the kind of workload that would age an SS TV. I'm currently trying to figure out an HV issue that brought it down a few weeks back.

Is the service switch on the back in the "normal" position? If not flip it there. Get a NOS vertical output tube and vert osc. tube (IIRC they are separate tubes in this chassis), there are a couple of lytics in the vertical that are suspect. When I get home I can post up a picture of the vertical section of the sam's provided my sam's covers that chassis, if not I believe I should have a Zenith issued print of that set's schematic (I have a fairly complete collection of Zenith color TV service lit). Would you like a set of legs for it? It was originally a legged console, and I happen to have a spare set of legs.

BTW: best way to work on the under chassis is to flip the set on it's side (make sure at least 2 of the 4 chassis mount screws with the nickel sized washers are installed first) and remove the bottom metal panel.

Notimetolooz
03-07-2017, 01:46 PM
damien191;
Well at least you know the CRT is in reasonable shape, no need to test that.
The Horizontal and HV sections are probably OK also. Any sound?
Troubleshooting is hard without enough test gear, but sometimes it can be done. If the horizontal line is very bright you should turn down the brightness.
TUD1;
I have two of the same Zenith radios, Royal 2000 and C725F.
Did you know that the Royal 2000 was the first American made, all transistor,
AM-FM, portable (battery) radio? At least that's what I've heard.

damien191
03-07-2017, 03:32 PM
Welcome to VK!

I have almost that EXACT Zenith and an identical Silvertone roundy (plus a second similar earlier Silvertone roundy). My Zenith is a 12B13C52 chassis (may be covered in the same sam's) in the same cabinet (which was called the Boyden BTW). That Zenith can be a real work horse...Mine has been my main TV for 8 years (of heavy service), and aside from small occasional maintenance (focus divider, tubes, a couple of vert stage caps, the H out tube socket) it took the kind of workload that would age an SS TV. I'm currently trying to figure out an HV issue that brought it down a few weeks back.

Is the service switch on the back in the "normal" position? If not flip it there. Get a NOS vertical output tube and vert osc. tube (IIRC they are separate tubes in this chassis), there are a couple of lytics in the vertical that are suspect. When I get home I can post up a picture of the vertical section of the sam's provided my sam's covers that chassis, if not I believe I should have a Zenith issued print of that set's schematic (I have a fairly complete collection of Zenith color TV service lit). Would you like a set of legs for it? It was originally a legged console, and I happen to have a spare set of legs.

BTW: best way to work on the under chassis is to flip the set on it's side (make sure at least 2 of the 4 chassis mount screws with the nickel sized washers are installed first) and remove the bottom metal panel.

thanks the schematic would be painfully helpful to me - then i can try to make sense of what I'm looking at, i have the legs i just took them off - two had been broken off when it was brought in by some poor handling... i have no idea what position is service and normal but in both positions it behaves the same way

i'm glad they're so reliable - i was wanting a good daily driver and the roundie thought neat has a bad flyback from a loose tube cap causing it to overheat - and it has a cataract that makes it hard to watch when it is working but im definitely not brave enough to tackle that - id never fine another one

damien191
03-07-2017, 03:33 PM
damien191;
Well at least you know the CRT is in reasonable shape, no need to test that.
The Horizontal and HV sections are probably OK also. Any sound?
Troubleshooting is hard without enough test gear, but sometimes it can be done. If the horizontal line is very bright you should turn down the brightness.
TUD1;
I have two of the same Zenith radios, Royal 2000 and C725F.
Did you know that the Royal 2000 was the first American made, all transistor,
AM-FM, portable (battery) radio? At least that's what I've heard.

there is sound, there's a faint... static? noise that comes from one of the tubes and goes up and down with it - i'm thinking tubes just need replaced since it was "thrown" off the back of a truck

Kamakiri
03-07-2017, 03:36 PM
By the way, welcome to the Zenith Color Commander Owner's Club! :D

damien191
03-07-2017, 03:43 PM
By the way, welcome to the Zenith Color Commander Owner's Club! :D

thanks! - looking at your picture reminds me my top dial light is out

Notimetolooz
03-07-2017, 09:12 PM
If it was thrown off a back of a truck there could be a lot of things broken.
Best not to turn any adjustments that you don't know what they do by the way. Some adjustments would require some expensive test equipment to set right again.

Electronic M
03-07-2017, 09:33 PM
My sam's don't cover that chassis (but the vert ckt may be the same)...I'm checking my zenith lit.

EDIT: I've got the Zenith issued schematic. Here are the PS and vert sections. C255, C258 and C259a would be my first suspects....55 or 58 caused very weak vert in my set.
https://c1.staticflickr.com/3/2899/32500929243_f2d0fbd6c1_z.jpg (https://flic.kr/p/RvZKX2)
https://c1.staticflickr.com/1/766/32500922033_7bfae02048_z.jpg (https://flic.kr/p/RvZHNH)

BTW: The "service" position of the service switch on the rear of the chassis is designed to collapse the vertical to a single horizontal line (for the procedure of setting the screen/G2 adjustments) and the "normal" position of the service switch is supposed to allow normal/full vertical deflection.

Good luck.

damien191
03-07-2017, 10:03 PM
OK, ill check those caps tomorrow - the garage light doesn't work and there's a ghost

since the switch literally does nothing i suppose i should check everything after that point

wait - is it just simple on/off switch and could i be lucky enough for a loose wire

Notimetolooz
03-08-2017, 01:07 PM
BTW: The "service" position of the service switch on the rear of the chassis is designed to collapse the vertical to a single horizontal line (for the procedure of setting the screen/G2 adjustments) and the "normal" position of the service switch is supposed to allow normal/full vertical deflection.

Good luck.

I believe the switch also decreases the brightness otherwise the screen would be burnt.
damien191, Normally that would be a problem if the vertical scan is lost because all the screen brightness would concentrated in one line.

DavGoodlin
03-08-2017, 04:26 PM
By the way, welcome to the Zenith Color Commander Owner's Club! :D

LOL - I too built a lazy-susan for my "color commander", in the attic waiting for a VDR and some free time to chase.